Induction device having a substantially pure sine relation between the coupling and the relative displacement of its elements



Dec. 26, 1950 J. P. GLASS. JR 2,535,914

INDUCTION DEVICE HAVING A SUBSTANTIALLY' PURE SINE RELATION BETWEEN THE COUPLING AND THE RELATIVE DISPLACEMENT OF ITS ELEMENTS Original Filed Aug. 21, 1944 7 Sheets-Sheet 1 RECEIVER I6 26 G AMPLIFIER 90 11 M455 5991'" 12 gwue/wtom JO/LIL R Glass,

wi M Dec. 26, 1950 J. P. GtASS, 2,535,914

' INDUCTION DEVICE HAVING A SUBST IALLY PURE SINE RELATION BETWEEN THE COUPLING AND THE RELATIVE DISPLACEMENT OF ITS ELEMENTS Original Filed Aug. 21, 1944 7 Sheets-Sheet 2 0055 N07 REL Y 0555 Y com/5c r/a/v o/v YCONNECT/ON 3 .fo/uz P Glasgfi:

Dec. 26, 1950 J. P. GLASS, JR 2,535,914

INDUCTION DEVICE HAVING A SUBSTANTIALLY PURE SINE RELATION BETWEEN THE COUPLING AND THE RELATIVE DISPLACEMENT OF ITS ELEMENTS Original Filed Aug. 21, 1944 7 Sheets-Sheet 5 RANSMITTER 3O RECEIVER 53 0055 NOT #5 L YON VCONNEC 770/V Dec. 26, 1950 J. P. GLASS, JR 2,535,914

INDUCTION DEVICE HAVING A SUBSTANTIALLY PURE SINE RELATION BETWEEN THE COUPLING AND THE RELATIVE DISPLACEMENT OF ITS ELEMENTS Joiua P Z5255, J

a /zux/i Dec. 26, 1950 J. P. GLASS, JR 2,535,914

INDUCTION DEVICE HAVING A SUBSTANTIALLY PURE SINE RELATION BETWEEN THE COUPLING AND THE RELATIVE DISPLACEMENT OF ITS ELEMENTS Original Filed Aug. 21, 1944 7 Sheets-Sheet 6 EXPERIMENTAL, JCOIL STATOR, 2 OPPO 5/ rs COILS I52 0N8-SLOT CYLINDR/CAL ROTOR.

COUPLING FACTOR COUPLING FACTO R.

NQE afa 631-8 7 5 s fi Joluz PGlass fr.

Dec. 26, 1950 J. P. GLASS, JR

INDUC ION DEVICE HAVING A SUBSTANTIALLY PURE SI RELATION BETWEEN THE COUPLING AND THE RELATIVE DISPLACEMENT OF ITS ELEMENTS Original Filed Aug. 21, 1944 7 Sheets-Sheet 7 40" RELATIVE snewms (55!: FIG. 20

gvwwwtoo -70/iu R Glass,.f1:

Patented Dec. 26, 1950 INDUCTION DEVICE HAVING A SUBSTAN- TIALLY PURE SINE RELATION BETWEEN THE COUPLING AND THE RELATIVE DIS PLACEMENT OF-ITS ELEMENTS John P. Glass, Jr., Haverford Township, Delaware County, Pa., minor to Bendix Aviation Corporation, Teterboro, N. 1., a

Delaware corporation of Original application August 21, 1944, Serial No. 550,461. Divided and this application January 5., 19.49, Serial No. 69,258

. 13 Claims. 1

This inventionrelates to the improvement of performance of electrical devices having relatively movable parts whether the latter are rotated or translated linearly from one position to another. It particularly relates to accurate telemetric servo-operation by simultaneous movements of rotors in transmitting and receiving devices, and especially when they are of the well known synchro" or self-synchronous motor type having S-phase stators.

This application is a division of my copending application Serial Number 550,461, filed August 21, 1944, now Patent 2,488,771, issued November 22. 1949.

A general object of the invention is to provide. with such devices, novel methods of and means for the production of substantially pure sinusoidal voltage and impedance variations with rotor angular position.

One specific object is to provide a highly accurate telemeter by the substantial elimination of errors due to rotor characteristics. Another is the improvement of accuracy by novel methods of and means for minimizing inaccuracies in telemetering due to the stators, said methods and means relating to the novel distributionvof the stator windings.

Another general object is to' provide electrical engineers with a new tool for use in predetermining the design of electrical devices having rotors to give optimum performance, which is important in either large or high-speed generators and motors, in pure sine generators, and'in telemeters of the self-synchronous type. I have found that the performance of both generators and motors is improved by the reduction to a minimum of the harmonic components which are generally attendated and lost in transmission with a corresponding loss in efliciency.

The above and other objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connectionwith the accompanying drawings. It is to be expressh' understood, however, that the drawings are for the purposes of illustration only and are not intended as a definition of the limits of the invention.

Heretofore it has been the practice to seek accuracy of telemetering by'making self-synchronous transmitters and receivers alike and relying upon the matching of their characteristics. But this practice has not proved adequate since practical manufacturing tolerances are too large for high accuracy unless special provisions are made. I have discovered that there are great advantages in telemetering obtained by minimizing departures from a pure sinusoidal output accordingto the present invention.

It is known that any graph of either voltage or impedance against either angular position or time may beanalyzed on the basis of a Fourier series with any desired degree of closeness by the use of a suflicient number of terms. In accordance with the present invention, there is provided a distribution of windings in the stator and/ or rotor to substantially eliminate all harmonics which could effect the performance. Further the invention includes a new technique in the use of the Fourier analysis to make possible for the first time the straight-forward design of such stators. e. g., instead of requiring the testing of a succession of experimental models. This approach of eliminating the harmonics by not forming them is more eflicient than any scheme, such as in, e. g.. the United States Patent 2,348,572 issued to P. H. Richardson, in which the harmonics are first formed and subsequently attenuated and wasted. And the techniques are radically different.

Before going into details, a general brief pre view is had of the instant approach. For example, by the use of a symmetrical 2-pole rotor, a stator coil voltage Es and its angle is may be represented by By sing a 31mm Sister, Y- necied; thesis and 9th harmonicscancel out as is gw n g The 9th harmonic also cancels out with 9.5mm

stators thus leaving the 5th and higher Harmonics with their amplitude diminishing rapidlyi gwith the number of harmonics. This leaves the 5th and 7th harmonics as the main sources of error. With a salient-pole rotor the 5th and 7th harmonies may'be substantially eliminated by tapering the pole faces consistent with their width.

But when a shaped pole rotor is used in a receiver .and for any reason its driving servo fails, said rotor introduces errors into the system which destroy the accuracy in other par allel receivera This makes a cylindrical nonsalient pole rotor highly desirable. Since stators having 2-pole rotors used only odd numbers of slots to minimize errors and, for non-split windings and ,3-phase stators. the number of slots would be odd integer-multiples of 3 and the possible number of slots in the stator would ;be 3, 9, 15.21, 27, 33, A

Taking, for example; a 9-slot stator and an 8- slot circular non-salient 2-pole rotor-with approximately one-slot relative skewing of stator and rotor. the number of bars in each slot may .be adjusted according to the present invention to give substantially complete elimination of the 5th and 7th harmonics. parallel coils. or equivalents. with unequal numbers of turns being thus used in the stator under the instant invention.

After reaching this concept. then from inspection of graphs of Es/Er for different rotor angles. where E- and Er are respectively the voltages across the stator (i. e. across the phase under consideration) and across the rotor. I changed the coil winding distribution from 100-50-for one phase to 80-50-20 (or about 53%, 33%, nil of the total turns per phase) with a marked improvement in the performance.

However. by my modification of the Fourier analysis, the percentages become 53.2. 34.7. 12.1 and the elimination of the 3rd through the 3th harmonics is substantially complete and independent of the characteristics for any symmetrical rotor. a matter of practical importance. This produces in a 3-phase self-synchronous servo-telemetric system both a much higher accuracy and a much lower residualgnull-voltage which permits the use of a much more sensitive servo-drive for the receiver. Further. by the Fourier analysis modified according to the present invention, with a9-slot stator. a 2-pole symmetrical rotor. and a Y-connection not desired, four coils may'be used with 34.7. 30.5. 22.7 and 12.1% of the total turns per phase with (due to symmetry about the 9th harmonic) negligible harmonics from the 3rd through the 15th, and no higher harmonics produced in appreciable amounts.

And, for special purposes. the requirements may similarly be met by the thus-modified Fourier analysis. For example. a virtually equal winding at right angles to the aforementioned parallel coils to provide two components at right angles. may be by a winding made of a ladder of split-coils halving the 34.7. 30.5. 22.7. 13.1% vaiues'noted earlier herein.

' The foregoing resume illustrates both the.

power and flexibility of the method of the present invention.

In the drawings. wherein like characters of reference indicate like parts throughout:

Figure 1 is a diagram of a conventional selfsynchronous servo-telemetric system;

Figure 10 isa similar graph for the 3-8101; pitch coil for several rotor widths and tapers;

Figure 11 is a diagram of a 9-slot stator showing a bar and the reference axis of the rotor:

Figure 12 is a graph showing the coupling factor for a phase and the fundamental and third harmonic plotted against time;

Figure 13 is a diagram for a 9-slot stator showing the position of the reference axis for symme y:

Figure 14 is a graph having the same coordinates'as Figure 12 but showing the fundamental Figure 2 is a diagram showing a typical stator with a conventional coil distribution. the coils having an equal number of turns and being progressively spaced by equal angles:

Figureiiisasimilardiagramshowingacommon distribution of like coils suitable for s-phase for the 4 slot pitch coil a-e with the fundamental shifted 10 and the third harmonic at 30 from the reference axis for Figure 13;

Figure 15 is a vector diagram forthe fundamental of the graph of Figure 14:

Figure 16 is a similar vector diagram for the third harmonic of Figure 14;

Figure 17 is a wiring diagram for a 7-slot single-phase rotor working in a 12-slot normal 2-phase stator with the rotor winding according to the invention: and

Figure 18 is a similar diagram. of .a salient 2-pole tapered rotor in a 3 -coil 3-slot stator with G-dummy-slots to, eilectively constitute a 9-slot stator.

Consider a well known self-synchronous servo telemeier with similar. except for the servo. transmitter and receiver units as. diagrammatically shown in Figure 1. A. 0. supply lines ii and is are connected with rotor coil ll of the transmitter and receiver units i5 and i5. Units ll and it respectively have'3 phases, ".15, II and II, It, 22 Y-connected by lines 33, 24, 25. The equilibrium position is shown. the receiver coil it being at right angles with the transmitter coll i3 and the flux in the receiver to minimise the voltage output of coil It. The zero reference position at the transmitter is E21: taken with coil i3 parallel with depending phase II, and thatjzu, for the receiver is normal to the plane of depending phase 20. In spite of the fact that rotor coils i3 and it do not have like positions even at this zero reference condition, I have discovered that pure sinusoidal outputs produce precisely equal angular movements of rotor coils i3 andit for equilibrium.

The two phase motor is operated in accordance with the phase diflerence of the amplified output of receiver rotor it from the A. 0. supply to produce the stated equilibrium condition. a 90' phase difference being provided, e. g.. in the amplifier.

Then, allowing for the 90' difference. the zero references nz and azican both be brought into parallelism with the depending phases i1 and 25 respectively of the transmitter and the a receiver for the purpose of determining telemetric error.

.Instead of having a single coil for each phase. actually a O-slot stator may be used with a plurality of coils per phase. These could be con- Figure tisacoil-dlstribution foraa-slotuventionallywoundasinligureaasfarasons assure Butter a 3-phase 9-slot stator, the coils are conventionally modified as in Figure 3 to have like coils for each phase by having each phase occupy one-third of the total number of slots, 3

"in this case. Thus we have coils -11, 0-9, and

(1-4:, each having 50 turns as in Figure 2.

As a matter 01' reducing the labor of winding and tying, but with no significant or perceptible change 01' the electro-magnetic eflect, these coils may be more or less conventionally rearranged, as shown in Figure 4, without changing the electrical characteristics of. the windingand hence without coming within the present invention. The ends of the bars which form the parallel coils may be reconnected to form equivalent coils in which the direction-sense oi the several bars is not altered, many alternative coll patterns being possible without affecting the electrical characteristics. The parallel coils are described both for the sake or clarity and as the preferred embodiment.

Coil c-h encloses 4 teeth in the shorter path and has 100 turns. Coil d-g similarly encloses 3 teeth and has 50 turns. This. arrangement has oblectionably large 5th and 7th harmonics present when a circular rotor is used, said harmonics respectively appearing in Equation 1 as Es sin 5 and E1 sin 7' As has earlier been noted, the 5th harmonic may be substantially eliminated and the 7th materially reduced by the use or a slight taper on the ends of the two salient poles. This feature will be considered further later herein and is considered to be one part of the invention.

- coil c-h.

But another, and commercially better, solution exists in another part of the invention. It was.

realized that, with a 9-slot stator, a maximum of four parallel coils can be used in each phase. The main point here is that a maximum'oi' only four independent coils per phase is possible in a 9-slot stator. As will be shown later for sub.- stantially complete elimination of the odd harmonies from the, 3rd through the th, the 3rd harmonic being eliminated without the use of a a-phase stator, N turns per phase in the coils, identified by the subscript using number of teeth performance obtained, including freedom-tram: 76 The any eii'ect due to the characteristics of a round rotor having two symmetrical poles, the rotor now being preferably oi. the non-salient pole type.

Also within the invention, I discovered that,

5 asinFigure6,asinglecoilcouldbeaddedto the two 0! Figure 4 with the same improvement in the performance, the principal dii'lerence being that the winding is simpler while equally eilective for a 3-phase Y-oonnected stator. The

10 winding relation is as follows:

Coils Percent Turns 2N4 34.73 54 2NI' 30.54 is 2N,- 22.67 34 2N 12.06 18 Both coils N1, for example may have 9 turns, coils N1, being coils c-d and g-h. This phase In other words, there has been dropped from Figure 5 the coil N1 which has the lowest coupling factor for the fundamental and is the most dimcult to install. 1

The addiiton of any N: coil to the phase wind-' ing or a 9-slot stator provides an improvement in direct ratio as the correct value of turns for N: is approached. A

Asomewhat difierent embodiment is shown in the common application of Figure '7 in which the transmitter 30 sets up sine and cosine components in the normal phases 3i and 32. Receiver 33 has like normal phases 34 and 35. The rotors I6 and 31 respectively for transmitter and receiver are connected with the common A. C. supply It with the result that an angular move- 5 ment of transmitter rotor 36 produces a like movement or receiver rotor 31 to a new equilibrium position as is well known.

Under the invention, one phase forv the 9-slot stator is made as shown in Figure 5 while the normal phase is made as the ladder coil of Figure 8. Due to the average angularity of the coils, approximately 1.5% more turns are needed. It is apparent from Figure 8 that the 4 coils'of 5 Figure 5 are split into 8 coils as iollowsi enjoys the same freedom from harmonics as that, shown in Figure 5, to which itis normal. By selecting a different total number of turns,

in the shorter path, is as follows expressed both correct percentages. in percent of the total number per phase and Referring to Figure 8, the coupling in one sense in the actual number of turns per phase: between the two phases in any given slot, e. g.

I slot e, is completely neutralized by identical coupling in the opposite sense in a complementary Pemnt slot, that in slot ,1. To avoid confusion, only M ans coil e! of the other phase is shown (dotted) in NlIII 30.54 40 Figure 8.

:--- fig; i: As earlier mentioned in connection with Figures 2-4, the 5th harmonic may be substantially eliminated by means of the right amount of taper for the width of face of a salient 2-pole rotor. Thus, referring to Figure 9, a taper of 0.005" is best for a rotor 010.322" width and 0.495" diameter with 0.0025" air-gap minimum.

graph on Figure 9 shows the voltage for the integer-turns more closely approximate the 9,680,014 g a v 7 theststorinpercentageofthatfortherctorfordifler'cnt positions of the rotor from the sen shown on its pilot diagram of the stator windings. Curve Arie. g.. shows the relationwith zero taper to beaten-sinusoidal with a stronaith harmonic while'icurve B: for the 0.005" tape rotor is a substantially pure sine. the curve for this coil which encloses 3 teeth in the shorter path being a fair average considering-the coupling weights of the several coils.- The other 3 curves contain substantial 3rd harmonics only. which. however. are neutralized by the Y-connection. 7

As earlier noted. this rotor is one means of carrying out the method of obtaining superior accuracy of telemetering by providing a substantially pure sinusoidal coupling between stator and rotor as the rotor's angular position changes. While deformed magnetic surfaces defining airgaps are well known in the motor and generator art. the use of precisely sine-matched taper and pole-width in self-synchronous telem'eters solved a problem which was long faced by skilled workers in this art.

Figure 10 is a similar graph in which the 3- tooth coil's voltage ratio is compared with a pure sine curve for several different tapers and two rotor widths. This shows that the earlier-stated rotor taper gives optimum performance and that it narrows the effective width of the rotor. In other words. a narrower rotor would require less taper.

The consideration of such graphs as that on Figure 9 also led to the production of a substantially pure sine relation by the addition of coil 2 with an adjustment of the number of turns in the other coils. as shown in Figure 6. This added means brought the circulating currents in the 3 phases into phase as regards time. when the rotors at transmitter and receiver are in correpedance of. a single bar inone stator slot of the ii-stot'stator, e. g.. of Figure 11. as the angular position of an undefined C. excited rotoris varied.- In Figure 12, the heavy curve shows the coupling of the bar to the rotor in volts per bar for 1 volt per'turn in-the rotor. Since the bar constltuteshalfofa turn. the maximum coupling factor thus expressed isapproximately one-half. The light curves show the fundamental and the strong 3rd harmonic components. r

This can be put into Fourier series form.

3= 'E'i sin Q-I-El' cos p-i-Ea sin 2+Es cos2 (2) and Figure 5 shows the four possible independent paralielcoils of'a 9-slot stator. Referring to Figure 13. the reference axis is chosen 00ln from slot 0 in order to,bring the axis parallel to the coils. wherein n is the number of stator slots.

As shown in Figure 14, this shifts the fundamental coupling curve of the bars in slot a 10' sponding positions. by eliminating the 5th and 7th harmonics from the impedances.

This also provided a better null-voltage since the poor null with conventional windings is duets the diiferenees of time-phase of these clrculating currents.

For example. with conventional stator windings. when the transmitter rotor was at 'from its zero reference. the receiver rotor was at 32' in equilibrium. .thus causing 2 error at null. This 2 nuil error was caused bythe stated odd harmonics. Under this condition. there existed 0.150 volt caused by the improper time-phasing of the circulating currents. This was objectionable because it kept the amplifier gain for the motor drive so low that the teiemeter was not sumciently sensitive to give optimum performance. By the means added under the invention. this null-voltage is reduced to less than onetenth of the 0.150 volt. value with a proportional increase in the possible gain and sensitivity and a proportional decrease in the error.

Once the foregoing approach is understood. one can modify the distribution of the turns in the several coils and experimentaly determine the closeness with which the truly sinusoidal relation is approached. making successive modifications under the invention until the required accuracy is-attained.

But while the foregoing procedure enables one to practice the invention. I have provided the following novel and more direct method of procedure. one which usefully eliminates successive cut-and-try approximations.

consider the voltage generated by. and the inand the fundamental coupling curve of the bars in slot e by 170' so that the coupling of coil (a -1V2. where (n-D/Z is the slot pitch. is

where N is the number of turns and the subscript is the slot pitch. For the fl-slot stator this factor is 2!: sin cm cos 10'. This fundamental coupling factor is shown in Figure 14 and in the vector form of Figure iii.

wiiliikewise the fundamental coupling factor in L? ll 2E1 llll Nu-a as shown in Equation '1.

900 90 E|=2Ei l h d i-4m 7+ Nun-am M 7+ an m g-{t 9 2:]

which roithe O-slot stator. reduces to sl=2srsinmwos 10'+Ns so-4- Na cos 50+N1 cos (a) Similarly for any harmonic h in the coupling curve of Figure. 12. the phase of the curve is shifted h 00'ln for the bars in slot n. Thus the 3rd harmonic of bars in slot 4 of 0-slot stator shwninl 'igure i-3isat8times' l0 orso' from theseroofthesrdharmoniccurve. Thesrd "'larmonicsofbarsiaslotsaandsareaddad 9 I vectoriaiiy as shown in Figure 16 so that the third harmonic in coil 4 of the. 9-slot stator is Ei=2E3 sin sow. cos so) (a) This may be stated generally for all harmonics asfollows:

From the above it is readily seen that any given harmonic may be suppressed in at least two dii'-. i'erent ways: either Ea sin hos may be made zero by modifying the rotor flux distribution or the term inside the bracket may be made zero by proper distribution of the turns in the stator slots in accordance with vEquation 10.

It should be noted that the stator and rotor members .may be interchanged or inverted so that a cylindrical rotor having an odd number of slots with a single .(or multiple) phase sine winding distributed as outlined above works with a stator having an even number of slots and very simple symmetrical windings. Such windings would be very advantageous when a large number of stator phases is desired.

In Figure 17, the rotor, instead of the stator, is wound non-harmonically under the invention while the stator. instead of the rotor, is symmetrical. For this example a-single phase winding is placed upon a 7-slot rotor using three parallel coils,.or equivalents, and two normalphase windings are placed on a l2-slot stator us ng two parallel coils per phase preferably each of 5-slot pitch.

p This construction of Figure 17 has the advantage that the rotor need not be so nearly sym metrical. a feature of practical importance for such applications as gyro-gimbal takesofl tra'ns-. mitter units. This illustrates the invertability of the rotor and stator.

Figure 18 relies on the shape of the rotor to provide a rotor-flux distribution which eliminates the 5th and 7th harmonics. The rotor and stator have 40 relative skew for the effectively 9-.slot stator, 6 dummy slots complementing 3 coilcontaining slots with the coils Y-connected to eliminate the 3rd harmonic. Thisconstruction permits the unit to be of minimum size under the invention to provide the substantially true sine relation which makes accurate telemetering possible with devices of the self-synchronous servotype'disclosed, the rotor faces being sinetapered. g

In the use of the modified Fourier procedure, a certain symmetry appears in eliminating harmonies above and below the nth harmonic where n is still thenumber of stator slots.

Consider the nth harmonic:

and for harmonic h"=n2 In this fashion if the Is" for any particular value of it less than n is made zero by distributing the winding to make the bracketed-term zero, then the summation value M for an equal order above n is also zero.

For example. with a 9-slot stator, where 81 gnrgade equal to zero, then E11 is likewise zero r1=2s1 sin um cos 70'+N: cos 21o-+ iv, cos sso-+zv1 cos 490) =0 (15) and En=2En 81h. 11(N4 00s +Na cos 330+ N: cos 550+Ni cos 770) =0 Noting that 2 cos 10 2X.9848 1.9696 1+cos 20 1+.9391 1.9397 In other words, the ladder-coil winding requires 1.5% more turns than its matching parallel-coil winding. While this eiiect issmall, its consideration helps one to perfect the winding distribution.

While generally less desirable, a stator and a rotor both having an even number of slots can be used under the invention by an extension of the foregoing procedure which is considerably extended because it requires consideration oi non-parallel coils and hence of both sine and cosine terms oi Eh- It is not given here because, since this extension involves no new principles, it may be carried out by one skilled in thi art after understanding the foregoing explanations. Likewise other generally undesirable ladder-type windings may be made for particular cases under the invention in stators having an odd number of slots.

From the foregoing it is manifest that the invention may be embodied in numerous and diverse "forms. For one example, it may be advantageously used with large alternators in which efliciency is raised by the production of a substantially pure sine wave with respect to time.

For another'it may be simply used with electrical elements which are relatively displaced in translation instead of rotation, e. g. pickups for operating working signals to moving trains. For still another it permits the more accurate modulation of a square-wave input voltage. It also has completely cured a long-standing difllculty withselb synchronous inductive servo systems due to they withno electrical load. 'This will be true regardless oi the'rotors shape and ilux distribution provided there are no abrupt changes producing appreciabletharmonics higher than those neutralized. For all practical rotors this condition is completely met. Only if the rotor is unskewed and 'subtends an extremely small are. i. e.. ilux concentrated angle less than 3.0", will the condition not be met. The only remain ng deviations are due to mechanical errors which ailect the symmetry and it is now possible in all practical cases to make the theoretical errors vanish into the mechanically produced background errors."

I! desired, a rotor, which has an odd number of slots wound to coniorm to the distribution tor harmonic elimination, may be used to proalso works out simply and advantageously for a 2-phase telemetric system or for resolvin angles into sine and cosine components.

l'or some purposes, e. g.. in a.,diilerentiai-type synchro. the invention may be practiced by using a rotor having a 3-phase v oonneoted winding which is symmetrical. in the plane of rotation. totwoaxesnormalbothtoeachotherandto theaxis c: rotation (e; g., like the stator winding oi Fig. 17) in a stator having a S-phase Y-connected stator winding with coils whose turns vary directly with the slot-pitch (e. g.. as in Figures 1, 5 and .6). Or the rotor and stator maybe inverted. p y

In the claims, "stator and rotor have been used to avoid ambiguity. these may accordingly be interchanged without ailecting their relative sunctionins.

If some other wave shape than the sinusoidal is it may be M by using my method. also the fundamental. may be suppressed and' a high harmonic'be produced by a low-speed generator under my invention.

Where a pair of polesisrete'rred toin the 'elaims. this may be one 0! a number of by-poles VII. 8. Patent 2.240.680 to Stuart and in general also has such a unitat the transmitter. However. the invention may be practiced with such a unit as one or the two telemetric units with the'other unit of another sort than that shown inU. 8. Patent 2.038.059.

Although only a few embodiments of the invention have been illustrated and described. various changes and modifications in the form and relative arrangement of the parts. which will now appear to those skilled in the art. may be made ot the invention. Reference is therefore to be also having 6 dummy slots. and a single-phase bisymmetrical rotor having 2 salient poles with the pole faces of eilectively 80 substantially in width andshaped to minimise the 5th and 7th harmonics. the rotor and stator havingeilectivelysubstantially relative skewing. whereby a closely sinusoidal relation is provided between the coupling and the relative angle between rotor andstator. v =4 2..A synchro unit comprising two inductive elements: a stator and rotor singularl movable with respect to said stator. said stator having 3- phase Y-connected windings. whereby the 3rd and 9th harmonics are neutralized. and 9 eti'ective equally spaced slots consisting of 3 cellsiots for said winding and 6 dummy slots. and said rotor being single-phase and bisymmetric'al and having 2 salient poles with the pole laces oi eii'ectiveiy substantially in width and shaped to have a closely arcuate peripheral profile normal to the axis of rotation with a radial leather at a width oi 80' equal to substantially twice the minimum radial clearance to minimize the 5th and 7th harmonics. the unit being constructed to have substantially 40' relative skewing between said elements, whereby a closely sinusoidal relation is provided between the coupling and the relative angle between rotor and stator.

3. The synchro unit set forth in claim 2. in which there is a departure from the stated width of pole face. and the proiile is changed to have a corresponding change 0! the radial feather. in

the same direction.

4. An inductive unit comprising two inductive elements or high permeability. constructed and arranged to be relatively movable without changing their distance apart. one oi said elements having 3-phase Y-connected windings in 3 coil-slots per cycle of a selected number at (:3 equally spaced slots per cycle with Sta-l) dummy slots per cycle,-whereby the 3rd and ,9th,harmonics are neutralized. and the other of said elements is constructed to have M salient poles with the pole laces eilectively of substantially cL/a: in width. i. e. in the direction of the stated move ment, where L is the distance in the direction of movement for a complete cycle and a. b. and c are small integers. each pole race being shaped to be symmetrical about its axis and with its proiile normal to thedireotion oi the stated relative movement substantially arcuate to provide an increase-of clearance or substantially twice the minimum value of said distance at a point L/9 lrom said axis of symmetry in the direction oi the stated relative movement. whereby the 5th and 1th harmonics are minimized. the two el ments being constructed to have [.734 eilective skewing. whereby a closely sinusoidal relation is provided between the coupling and the stated relative movement. j p

5. An inductive unit as set forth-in claim 4 in which a is odd.

6. An inductive unit comprising two relatively movable elements or high permeability. .constructed and arranged to .be relatively movable without changing theirdistance apart, one of said elements having d-phase 'Y-connected windwith ilt pai' s iron the spirit or the sc p 7 6 ings in l coil-slots per cycle, whereby the 3rd and 9th harmonics are neutralized and also having 3e dummy slots per cycle, where e is a small integer, with the effective slots substantially equally spaced, the other of said elements is constructed to have b2 salient poles with the pole faces effectively of substantially cL/3(1+e) in width, i. e. in the direction of the stated movement, where L is the distance in the direction of the stated movement for a complete cycle and b and c are small integers, and each pole face is shaped to be symmetrical about its axis and with its profile, normal to the direction of the stated relative movement, substantially arcuate to provide an increase of clearance of substantially twice the minimum value of said distance at a point L/9 from said axis of symmetry in the direction of the stated relative movement, whereby the 5th and 7th harmonics are minimized, and the two elements are constructed to have L/3(1+e) effective skewing, whereby a closely sinusoidal relation is provided between the coupling and the stated relative movement.

7. A synchro unit comprising a stator having 3-phase Y-connected windings in 3 coil-slots and also having 3e dummy slots, where e is a small integer, whereby the 3rd and 9th harmonics are neutralized, and a single-phase bisymmetrical rotor, whereby all even harmonics are neutralized. having b2 salient poles with the pole faces of effectively c120/ (1+e) substantially in width, where b and c are small integers, and shaped to have a closely arcuate peripheral profile normal to the direction of the axis of rotation with a radial feather at a point 40 from the axis of bisymmetry equal to substantially twice the minimum radial clearance to minimize the 5th and 7th harmonics, the rotor and stator being constructed to have substantially 120/(1+e) effective relative skewing, whereby a closely sinusoidal relation is provided between the coupling and the relative angle between rotor and stator.

8. The synchro unit set forth in claim 7, in which there is a departure from the stated width of pole face and the profile is changed to have a corresponding change of radial feather in the same direction.

9. A synchro unit comprising two inductive elements: a, stator and a rotor angularly movable with respect to said stator, said stator having 3-phase Y-connected windings, whereby the 3rd and 9th harmonics are neutralized, in 3 coilslots and also having 3e dummy slots to constitute 3 (l-i-e) effective slots, where e is a small integer, and a bisymmetrical rotor, whereby all of the even harmonics are neutralized, constructed to minimize the other low-order odd harmonics.

10. The synchro unit set forth in claim 9, in which the unit is constructed to have one effective slot pitch relative skewing between said elements.

11. A synchro unit comprising two relatively movable elements of high permeability which are constructed and arranged to be relatively movable without changing their distance apart, one of said elements having 3-phase Y-connected windings, whereby the 3rd and 9th harmonics are neutralized, in 3 coil-slots and is constructed to have 3e dummy slots per cycle to constitute 3 (1+e) effective slots, where e is a small integer, and the other of said elements is constructed to be bisymmetrical, whereby all of the even harmonies are neutralized, and is modified to minimize the other low-order harmonics, whereby a closely sinusoidal relation is provided between the coupling and the stated relative movement between said elements.

12. A synchro unit as set forth in claim 11, in which the unit is constructed to have one effective slot-pitch relative skewing between the two elements.

13. A synchro unit having two elements of high permeability, constructed and arranged to be angularly relatively movable and to have one effective slot-pitch relative skewing, one element being constructed to be bisymmetrical and the other to be symmetrical about an axis normal to that of rotation, and either element being shaped to minimize at least two odd, low-order harmonics and the other element being constructed to include dummy slots with all effective slots equally spaced, whereby the order of the harmonic ins troduced by the coil-containing slots is raised with a consequent proportional reduction of the magnitude of both said harmonic and the stated relative skewing.

JOHN P. GLASS, JR.

No references cited. 

